First Spectrum of Comet C/1996 B2 Hyakutake

First Spectrum of Comet C/1996 B2 (Hyakutake)

ESO Press Photo 12/96; 11 February 1996

This diagramme shows the first spectrum obtained of comet C/1995 B2 (Hyakutake),
which is expected to pass near the Earth in late March 1996. It was taken by Tomaz
Zwitter, visiting astronomer at the ESO La Silla Observatory from the University of
Ljubljana, Slovenia. It has been flux- [log(erg/s/cm2/A) within 2x14 arcsecond slit
centered on comet] and wavelength- [Angstrom] calibrated.

The following description of this spectrum was published on IAU Circular 6306
(February 9, 1996):

T. Zwitter and H. Mikuz, University of Ljubljana; and U. Munari and M.
Rejkuba, Asiago Observatory, communicate: 'A spectrogram (range 340-910
nm) of C/1996 B2 was obtained at the European Southern Observatory's
1.5-m telescope (+ Boller & Chivens spectrograph + CCD) on Feb. 8.2 UT.
The slit (width 2 arcsec, length 14 arcsec) was positioned on the comet
nucleus. The reflected solar spectrum accounts for the vast majority of the
recorded flux, with all major absorption lines markedly visible. The strongest
cometary emission is from CN(0,0) at 388 nm, followed by the C3 complex at
405 nm. The strongest C2 Swan band is that of (0,0) at 516 nm, followed by that
of (1,0) at 474 nm, with that of (2,0) at 438 nm being barely detectable. The
CN(0,1) 422-nm band is in moderate emission, while no cometary NaI D
emission is observed.

At the time of this observation, the comet was at a distance of 1.55 AU (232 million
kilometres) from the Earth and 1.89 AU (283 million kilometres) from the Sun.
The recorded spectrum is typical for a comet at this heliocentric distance.

This is the caption to ESO PR Photo 12/96. It may be reproduced, if credit is given
to the European Southern Observatory.